Extracorporeal blood treatment involves removing blood from a patient, treating the blood external to the patient and returning the treated blood to the patient. Occasionally, bubbles form in the blood during extracorporeal blood treatment as a result of leakage of air into the blood at the point blood is withdrawn from the patient for extracorporeal treatment and as a result of leakage of air at points of connection in the extracorporeal treatment system. Bubbles also form as a result of turbulence of the blood flowing in the extracorporeal treatment system and coalescence of gases in the blood during treatment, among other causes. Care must be taken to remove bubbles from the blood prior to returning the blood to the patient and, to the extent possible, prevent formation of bubbles in the blood during treatment. Blood returned to the patient which contains bubbles creates a risk of serious health consequences to the patient.
Sometimes bubbles in blood flowing through extracorporeal treatment systems are optically or sonically detectable and many such systems incorporate equipment capable of detecting these bubbles. When bubbles are detected, the flow of blood returning to the patient is usually halted to prevent return of the detected bubbles to the patient. However, it is preferable that such bubbles be collected and removed from the blood so that blood treatment can continue uninterrupted.
Most extracorporeal treatment systems incorporate chambers for removal of bubbles from blood undergoing treatment. These chambers, often referred to as bubble traps, provide an opportunity for bubbles in the blood to separate from the blood while the blood is in the chamber. Bubbles in the blood rise to the surface of the blood in the chamber. Bubbles in the blood may also separate from the blood as the blood is delivered to the chamber, when the blood is delivered dropwise or in a stream over the surface of the blood already present in the chamber. The gas from the bubbles which collects above the level of blood is mechanically removed from the chamber, or is allowed to remain in the chamber until extracorporeal treatment is complete.
It is possible, however, that smaller bubbles may be present in the blood which may not be collected in the bubble traps of some extracorporeal treatment systems. The patient may then be subject to a risk of injury when these smaller bubbles coalesce into a larger bubble upon aggregation of the bubbles within the patient or may be subject to other risks.
Conditions under which bubbles form in the blood during extracorporeal treatment may be exacerbated by higher blood flow rates. For example, blood entering a bubble trap apparatus at a high rate may froth and create bubbles in the blood present in the bubble trap apparatus. These bubbles could pass through the bubble trap apparatus and remain in the blood to be returned to the patient.
Poor flow patterns can also create problems for blood flowing through a bubble trap apparatus. For example, if blood flow in a bubble trap apparatus is excessively turbulent, the blood's clotting processes may be activated undesireably and blood clots may form in the blood. Also by way of example, incomplete mixing of blood can cause blood in portions of the bubble trap apparatus to stagnate. The stagnated blood is then susceptible to clotting. Clotting of blood in a bubble trap apparatus may result in occlusion of lines of the extracorporeal blood treatment system or injury to the patient.
When blood is introduced into a bubble trap apparatus below the upper surface of the blood already present in the apparatus, stagnation and clotting have a tendency to occur in the blood near the upper surface of the blood. Stagnation and clotting occur near the upper surface of blood because the newly introduced blood tends to flow downward and often does not mix with blood above the point of introduction and near the upper surface. Although these clots may be filtered out of the blood before the blood is returned to the patient, excessive clot formation can occlude filters, which can lead to decreased blood flow to the patient.
One way that clot formation has been minimized is by introducing additional heparin into the blood of the patient. However, excess heparin in a patient can lead to other health problems and therefore excessive use of heparin is not preferred.
It is against this background that the significant improvements and advancements of the present invention have taken place.